Electric compressor

ABSTRACT

A compressor includes a motor unit formed of a stator and a rotor, a compressor mechanism driven by the motor unit, and an enclosed container accommodating the foregoing elements. The compressor mechanism includes a cylinder block equipped with a compressing chamber and a piston. A shaft directly coupled to the rotor that drives the piston is supported by a double-sided bearing system, namely, a main bearing and a sub bearing. This structure allows preventing the shaft from slanting, and reducing a loss and a noise caused by sliding. As a result, a low profile, highly reliable and efficient compressor is obtainable.

FIELD OF THE INVENTION

[0001] The present invention relates to electric compressors used in refrigerators with freezers or air-conditioners.

BACKGROUND OF THE INVENTION

[0002] An electric compressor (hereinafter referred to simply as a compressor) employed in freezers of home-use refrigerators has undergone improvements for more efficient performance, such as use of lubricant oil of lower viscosity, use of inverter driving, and employment of synchronous motor. Those improvements have been done for reducing power consumption of the compressor. At the same time, the compressor is required to be more compact for increasing a volume efficiency of the refrigerator.

[0003] A conventional compressor is disclosed, e.g. in Japanese Patent Application Non-Examined Publication No. 2001-73948. This compressor is improved its stator and main bearing. FIG. 5 shows a vertical sectional-view of this compressor. In FIG. 5, enclosed container 1 of the compressor pools lubricant oil 12 at its bottom section. Container 1 accommodates motor unit 3 formed of stator 13 and rotor 14, and compressor mechanism 2 driven by motor unit 3.

[0004] Compressor mechanism 2 is detailed hereinafter. Cylinder block 5, forming generally cylindrical cylinder 7, is equipped with bearing 6 which rotatably supports shaft 4 and crosses with cylinder 7 at approx. right angles. Bearing 6 is made of aluminum-based material, i.e. non-magnetic material. Shaft 4 is equipped with eccentric section 4 a and inserted into bearing 6. Rotor 14 is rigidly mounted to shaft 4.

[0005] Piston 9 slides in cylinder 7 and forms compressing chamber 10, and it is coupled to eccentric section 4 a via connecting rod 8 which works as a linking means. Lubricating tube 11 is mounted to a tip of eccentric section 4 a.

[0006] Next, motor unit 3 is detailed hereinafter. Motor unit 3 is a two-pole induction motor comprising stator 13 and rotor 14. Stator 13 is formed by winding wires on a stator iron-core made of laminated electromagnetic steel plates, and rotor 14 is formed of rotor iron-core 15 having interior permanent-magnet 15 b. Rotor iron-core 15 has hollow bore 16 at its end face on compressor mechanism 2 side, and bearing 6 extends into bore 16.

[0007] An operation of the foregoing conventional reciprocating compressor is described hereinafter. Rotation of rotor 14 entails shaft 4 to spin, and the rotation of eccentric section 4 a of shaft 4 is transferred to piston 9 via connecting rod 8, so that piston 9 reciprocates in compressing chamber 10. This operation sucks refrigerant gas supplied from a cooling system (not shown) into compressing chamber 10, then compresses the gas, and discharges successively the gas to the cooling system again such as a refrigerator or an air-conditioner.

[0008] The rotation of shaft 4 causes lubricating tube 11 placed at the lower end of shaft 4 to rotate, so that lubricant oil 12 is drawn up by pumping operation due to the centrifugal force of tube 11. As a result, bearing 6, cylinder 7, connecting rod 8 and piston 9 are lubricated.

[0009] The foregoing structure; however, produces magnetic attraction that attracts rotor 14 to a space of shorter distance if the distance between rotor 14 and stator 13 is not uniform (eccentric). In particular, when permanent magnet 15 b built-in rotor iron-core 15 is made of rare-earth material, i.e. the magnet has intense magnetic force, the greater magnetic attraction is produced at a greater eccentricity of the space.

[0010] As a result, shaft 4 inserted in bearing 6 slants and hits against bearing 6. If shaft 4 rotates within bearing 6 in this condition, the sliding faces of both bearing 6 and shaft 4 sometime incur abrasion.

[0011] Another prior art of the foregoing conventional compressor discloses a structure where an end-face of a main bearing made of iron-based material is not laid over an end-face of a rotor iron core on a compressor mechanism side. In this case, if bearing 6, i.e. single-sided bearing, maintains the necessary bearing length, a total length of shaft 4 is obliged to increase, which entails a longer distance between bearing 6 and the gravity center of rotor 14. As a result, abrasion sometimes occurs on the sliding faces of both bearing 6 and shaft 4. This is because the magnetic attraction produced between rotor 14 and stator 13 works as strong moment within bearing 6, so that shaft 4 hits more strongly against bearing 6.

SUMMARY OF THE INVENTION

[0012] The present invention addresses the problems discussed above, and aims to provide a highly reliable and efficient compressor. The compressor of the present invention comprises the following elements:

[0013] (a) a motor unit including a stator with windings, and a rotor with a rotor iron-core and a permanent magnet;

[0014] (b) a compressor mechanism driven by the motor unit and including the following sub-elements;

[0015] (b-1) a shaft including an eccentric shaft section, a main shaft section and a sub shaft section, the main shaft section and the sub shaft section sandwiching the eccentric shaft section vertically and being placed coaxially;

[0016] (b-2) a cylinder block including a compressing chamber;

[0017] (b-3) a main bearing, disposed in the cylinder block such that the main bearing crosses with an axial core of the compressing chamber at right angles, for rotatably supporting the main shaft section;

[0018] (b-4) a sub bearing, disposed in the cylinder block, for rotatably supporting the sub shaft section;

[0019] (b-5) a piston for reciprocating in the compressing chamber;

[0020] (b-6) a linking means for coupling the piston with the eccentric shaft section; and

[0021] (c) an enclosed container for pooling lubricant oil and accommodating the motor unit and the compressor mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 shows a vertical sectional view of a compressor in accordance with a first exemplary embodiment of the present invention.

[0023]FIG. 2 shows a vertical sectional view of a compressor in accordance with a second exemplary embodiment of the present invention.

[0024]FIG. 3 shows a vertical sectional view of a compressor in accordance with a third exemplary embodiment of the present invention.

[0025]FIG. 4 shows a vertical sectional view of a compressor in accordance with a fourth exemplary embodiment of the present invention.

[0026]FIG. 5 shows a vertical sectional view of a conventional compressor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0027] Exemplary embodiments of the present invention are demonstrated hereinafter with reference to the accompanying drawings.

Exemplary Embodiment 1

[0028]FIG. 1 shows a vertical sectional view of a compressor in accordance with a first exemplary embodiment of the present invention. In FIG. 1, enclosed container 101 accommodates compressor mechanism 102 and motor unit 103 that drives the compressor mechanism. The refrigerant filled in container 101 is a hydrocarbon refrigerant such as R134a of which ozone-destroying coefficient is zero (0), or R600a having a low global-warming coefficient. Container 101 also pools lubricant oil 112 mutually soluble with the refrigerant and having viscosity of 5-10 [cts] at its bottom.

[0029] Next, compressor mechanism 102 is detailed hereinafter. Shaft 104 includes eccentric shaft section 117, main-shaft section 116 and sub-shaft section 118. Main-shaft section 116 and sub-shaft section 118 sandwich eccentric shaft section 117 vertically and are disposed coaxially. Lubricating mechanism 111 formed on shaft 104 communicates into lubricant oil 112 at its first end and communicates with the upper end of shaft 104 to open at its second end.

[0030] Cylinder block 105 is made from cast-iron, and is integrally formed of cylindrical compressing chamber 110 and main bearing 120 which rotatably supports main shaft section 116. Sub-bearing 121 rotatably supporting sub-shaft section 118 is fixed to cylinder block 105. Piston 109 is inserted into compressing chamber 110 in a slidable manner. Connecting rod 108 working as a linking means couples piston 109 with eccentric shaft section 117.

[0031] Motor unit 103 is detailed hereinafter. It is an inverter-driven motor formed of stator 113 and rotor 114, and driven at any plural frequencies such as 30 Hz, 50 Hz, 70 Hz, and 80 Hz. Stator 113 is constructed as this: a plurality of teeth 113 b radially formed is disposed at iron core 113 a, and windings 113 d are provided to teeth 113 b via insulating material 113 c to form a motor of a concentrated winding structure. Rotor 114 is fixed to main-shaft section 116 of shaft 104 and includes permanent magnet 115 a built in rotor iron-core 115. Permanent magnet 115 a is made of, e.g. rare-earth magnet such as neodymium, iron, boron-based ferromagnetic materials.

[0032] Assume that there is a virtual plane which includes end section 115 b of rotor iron-core 115 on the compressor mechanism side and is generally orthogonal to the axial core of main shaft section 116. Main bearing 120 is structured so as not to cross with this virtual plane.

[0033] An operation of the compressor discussed above is demonstrated hereinafter. When a current runs through stator 113, rotor 114 spins shaft 104, and eccentric motion of eccentric shaft section 117 is transferred to piston 109 via connecting rod 108, thereby reciprocating piston 109 in compressing chamber 110. This operation sucks the refrigerant gas from the cooling system (not shown) to chamber 110, and compresses the gas, then discharges the gas to the cooling system again.

[0034] Lubricating mechanism 111 formed on shaft 104 pumps up lubricant oil 112, which is then discharged from an upper end of shaft 104.

[0035] Permanent magnet 115a built in rotor iron-core 115 is made of, e.g. rare-earth material having intense magnetic force, so that it produces extraordinary intense magnetic attraction at a place where a distance between rotor 114 and stator 113 is small.

[0036] However, when shaft 104 of this structure receives an unbalanced load caused by the magnetic attraction generated between rotor 114 and stator 113, a distance between two fulcrums is approx. doubled comparing with the conventional structure discussed previously. Because in the case of the conventional structure, the single-sided bearing receives the unbalanced load at its upper and lower ends as the fulcrums arranged in the diagonal direction with respect to the center axis of shaft 104 placed in the inner wall of the main bearing. On the other hand, a double-sided bearing employed in the structure of the first embodiment receives the unbalanced load at its inner wall end on the counter side to the sub-bearing and at an inner wall end of the sub-bearing on the counter side to the main bearing along a diagonal direction with respect to the axis center of shaft 104.

[0037] The extension of the distance between the fulcrums reduces a slant angle of shaft 104 within the bearing, so that shaft 104 scarcely hits against the bearing. As a result, sliding loss due to the hitting can be prevented and the compressor can maintain efficient operation. At the same time, a sliding noise due to the hitting can be suppressed, so that a compressor with a lower noise is obtainable. The load to shaft 104 in operation is received at eccentric shaft section 117 (fulcrum) as a center, to which a compressing load from piston 109 is applied, and upper and lower ends, so that the load can be distributed generally even to this fulcrum. Comparing with the single-sided bearing, in which the load concentrates on its one end, the sliding face of shaft 104 has better reliability.

[0038] Shaft 104 receives the load in operation at its wide area with little interference with the bearing, so that contact pressure of main bearing 120 and sub bearing 121 lowers, which can shorten the length of main bearing 120. As a result, the total height of the compressor can be lowered. Further, a reduction of the sliding length can lower viscosity resistance at the sliding section, so that the efficiency is improved.

[0039] Main bearing 120 is integrally formed with cylinder bock 105, i.e. made of cast-iron that is iron-based material, however, since bearing 120 is placed so as not to touch at rotor iron-core 115, the magnetic flux of permanent magnet 115 a built in iron-core 115 seldom interferes with main bearing 120. As a result, eddy-current loss scarcely occurs in the main bearing, and the higher efficiency can be expected.

[0040] Motor unit 103 is inverter-driven, so that it is driven at a high frequency such as 70-80 Hz in response to the load. At that time, motor unit 103 produces strong magnetic attraction, which tends to slant shaft 104; however, since shaft 104 is supported by the double-sided bearing, i.e. main bearing 120 and sub bearing 121, shaft 104 is prevented from slanting, and at the same time, sliding loss can be reduced. As a result, the compressor can maintain efficient operation, and prevent the shaft from hitting against the bearing, so that the reliability can be improved.

[0041] When motor unit 103 is driven at a low frequency such as 30 Hz, the double-sided bearing structure prevents shaft 104 from slanting because shaft 104 is supported by main bearing 120 and sub bearing 121, so that the sliding loss can be reduced. Thus use of lubricant oil 112 of low viscosity such as 5-10 [cts] can assure the reliability.

[0042] Stator 113 includes plural teeth 113b radially formed in iron-core 113 a, and windings are provided to teeth 113 b via insulating member 113 c. This structure eliminates a coil-end which is needed in the distributed winding structure. As a result, the total heights of stator 113 and rotor 114 can be lowered, so that the total height of the compressor can be further lowered. The low profile of stator 113 and rotor 114 facilitates uniforming the clearance between stator 113 and rotor 114. As a result, the magnetic attraction rarely occurs, so that an increase of an input current due to interference between stator 113 and rotor 114 as well as an increase of a noise can be avoided.

[0043] In this embodiment, connecting rod 108 is used as the linking means for coupling the piston with the eccentric shaft; however, a ball joint or a Scotch yoke can be used as the linking means.

Exemplary Embodiment 2

[0044]FIG. 2 shows a vertical sectional view of a compressor in accordance with the second exemplary embodiment of the present invention. Similar elements to those in the first embodiment have the same reference marks, and the detailed descriptions thereof are omitted here. In FIG. 2, motor unit 203 is a two-pole synchronous motor comprising the following elements:

[0045] stator 213 formed of a stator iron-core wound with windings, the iron-core being formed by laminating electromagnetic steel sheets, and

[0046] rotor 214 formed of rotor iron-core 215 equipped with a secondary conductor, iron-core 215 being formed by laminating electromagnetic steel sheet.

[0047] Rotor iron-core 215 incorporates permanent magnet 215 a made of, e.g. neodymium of rare-earth magnet, iron, boron-based ferromagnetic materials. Other structures remain unchanged as the first embodiment.

[0048] An operation of the foregoing compressor is demonstrated hereinafter. Motor unit 203 starts working as an induction motor, and when it comes around the synchronizing rpm, synchronous pull-in is carried out for synchronous operation.

[0049] Since permanent magnet 215 a is made of ferromagnetic material having intense magnetic force, it produces extraordinary intense magnetic attraction at the place where a clearance between rotor 214 and stator 213 is small. However, the same structure as that in the first embodiment can overcome this problem. As a result, highly efficient operation of the synchronous motor is advantageously used for obtaining high energy efficiency. At the same time, the shaft of the compressor is prevented from hitting the bearing due to slant, so that the reliability can be improved.

Exemplary Embodiment 3

[0050]FIG. 3 shows a vertical sectional view of a compressor in accordance with the third exemplary embodiment of the present invention. Similar elements to those in the first embodiment have the same reference marks, and the detailed descriptions thereof are omitted here.

[0051] In FIG. 3, enclosed container 101 accommodates compressor mechanism 302 and motor unit 303 that drives this compressor mechanism. Cylinder block 305 of compressor mechanism 302 is made from cast-iron and forms cylindrical compressing chamber 110. Main bearing 320 for rotatably supporting main shaft section 116 of shaft 104 and sub-bearing 121 for rotatably supporting sub-shaft section 118 are rigidly mounted to cylinder block 305.

[0052] Motor unit 303 comprising stator 113 and rotor 314 is an inverter-driven motor that is driven at plural frequencies. Rotor 314 is fixed to main-shaft section 116 of shaft 104 and includes permanent magnet 315 a built in rotor iron-core 315. Permanent magnet 315 a is made of, e.g. rare-earth magnet such as neodymium, iron, boron-based ferromagnetic materials. Rotor iron-core 315 has hollow bore 306 at its end face on compressor mechanism 302 side. Main bearing 320 is made from aluminum alloy which is non-magnetic material, and extends into bore 306.

[0053] An operation of the foregoing compressor is described hereinafter. When a current runs into stator 113, rotor 314 spins shaft 104, and eccentric motion of eccentric shaft section 117 is transferred to piston 109 via connecting rod 108, so that piston 109 reciprocates in compressing chamber 110. This operation sucks refrigerant gas supplied from a cooling system (not shown) into compressing chamber 110, then compresses the gas, and discharges the gas into the cooling system again. Lubricating mechanism 111 formed on shaft 104 pumps up lubricant oil 112, which is then discharged from an upper end of shaft 104.

[0054] Permanent magnet 315 a built in rotor iron-core 315 is made of, e.g. rare-earth material having intense magnetic force, so that it produces extraordinary intense magnetic attraction at a place where a clearance between rotor 314 and stator 113 is small.

[0055] When shaft 104 of this structure receives an unbalanced load caused by the magnetic attraction generated between rotor 314 and stator 113, a distance between two fulcrums becomes far longer than that of the conventional structure discussed previously. On top of that, since main bearing 320 extends into bore 306, the distance between the fulcrums becomes further longer. Because in the case of the conventional structure, the single-sided bearing receives the unbalance load at its upper and lower ends as fulcrums arranged in the diagonal direction with respect to the center axis of shaft 104 placed in the inner wall of the main bearing. On the other hand, the double-sided bearing employed in this third embodiment receives the unbalanced load at the following two fulcrums: its inner wall end on the counter side to the sub-bearing and at an inner wall end of the sub-bearing on the counter side to the main bearing along a diagonal direction with respect to the axis center of shaft 104.

[0056] The extension of the distance between the fulcrums reduces a slant angle of shaft 104 within the bearing, so that shaft 104 scarcely hits against the bearing. As a result, sliding loss due to the hitting can be prevented and the compressor can maintain efficient operation. At the same time, a sliding noise due to the hitting can be suppressed, so that a compressor with a lower noise is obtainable. The load to shaft 104 in operation is received at eccentric bearing 117 (fulcrum) as a center, to which a compressing load from piston 109 is applied, and upper and lower ends, so that the load can be distributed generally even to this fulcrum. In comparison with the single-sided bearing, in which the load concentrates on its one end, the sliding face of shaft 104 has better reliability.

[0057] Since main bearing 320 is made of aluminum alloy, i.e. non-magnetic material, permanent magnet 315 a built in rotor iron-core 315 does not produce eddy-current. Thus eddy-current loss can be eliminated, and high efficiency can be achieved.

[0058] Motor unit 303 is inverter-driven, so that it is driven at a high frequency in response to the load. At that time, motor unit 303 produces strong magnetic attraction, which tends to slant shaft 104; however, since shaft 104 is supported by the double-sided bearing, i.e. main bearing 320 and sub bearing 121, shaft 104 is prevented from slanting, and at the same time, sliding loss can be reduced. As a result, the compressor can maintain efficient operation, and prevent the shaft from hitting against the bearing, so that the reliability can be improved.

[0059] Stator 113 includes plural teeth 113 b radially formed in iron-core 113 a, and windings 113 d are provided to teeth 113 b via insulating member 113 c. This structure eliminates a coil-end which is needed in the distributed winding structure. As a result, total heights of stator 113 and rotor 314 can be lowered, so that the total height of the compressor can be further lowered. The low profile of stator 113 and rotor 314 facilitates uniforming the clearance between stator 113 and rotor 314, and as a result, the magnetic attraction rarely occurs, so that an increase of an input current due to interference as well as an increase of noise can be avoided.

Exemplary Embodiment 4

[0060]FIG. 4 shows a vertical sectional view of a compressor in accordance with the fourth exemplary embodiment of the present invention. Similar elements to those in the third embodiment have the same reference marks, and the detailed descriptions thereof are omitted here.

[0061] In FIG. 4, motor unit 403 is a two-pole synchronous motor comprising the following elements:

[0062] stator 213 formed of a stator iron-core wound with windings, the iron-core being formed by laminating electromagnetic steel sheets, and

[0063] rotor 414 formed of rotor iron-core 415 equipped with a secondary conductor, iron-core 415 being formed by laminating electromagnetic steel sheets,

[0064] Rotor iron-core 415 incorporates permanent magnet 415 a made of, e.g. neodymium of rare-earth magnet, iron, boron-based ferromagnetic materials. Other structures remain unchanged as the third embodiment.

[0065] An operation of the foregoing compressor is demonstrated hereinafter. Motor unit 403 starts working as an induction motor, and when it comes near the synchronizing rpm, synchronous pull-in is carried out for synchronous operation. Since permanent magnet 415 a is made of ferromagnetic material having intense magnetic force, it produces extraordinary intense magnetic attraction at the place where a clearance between rotor 414 and stator 213 is small.

[0066] However, the same structure as that in the third embodiment can overcome this problem. As a result, highly efficient operation of the synchronous motor is advantageously used for obtaining high energy efficiency. At the same time, the shaft of the compressor is prevented from hitting the bearing caused by the slant, so that the reliability can be improved. 

What is claimed is:
 1. An electric compressor comprising: (a) a motor unit including a stator with a winding, and a rotor with a rotor iron-core and a permanent magnet; (b) a compressor mechanism driven by the motor unit and including: (b-1) a shaft including an eccentric shaft section, a main shaft section and a sub shaft section, the main shaft section and the sub shaft section sandwiching the eccentric shaft section vertically and being placed coaxially,; (b-2) a cylinder block including a compressing chamber; (b-3) a main bearing, disposed in the cylinder block such that the main bearing crosses with an axial core of the compressing chamber at right angles, for rotatably supporting the main shaft section; (b-4) a sub bearing, disposed in the cylinder block, for rotatably supporting the sub shaft section; (b-5) a piston for reciprocating in the compressing chamber; (b-6) a linking means for coupling the piston with the eccentric shaft section; and (c) an enclosed container for pooling lubricant oil and accommodating the motor unit and the compressor mechanism.
 2. The compressor of claim 1, wherein the main bearing does not cross with a plane which includes an end section of rotor iron-core on the compressor mechanism side and is orthogonal to an axial core of the main shaft section.
 3. The compressor of claim 2, wherein the main bearing is made of iron-based material.
 4. The compressor of claim 1, wherein the rotor iron-core has a hollow bore at its end section on the compressor mechanism side, and the main bearing extends into the bore.
 5. The compressor of claim 4, wherein the main bearing is made of non-magnetic material.
 6. The compressor of claim 1, wherein the permanent magnet is made of rare-earth material.
 7. The compressor of claim 1, wherein the motor unit is driven at a plurality of frequencies including a frequency not lower than a commercial power frequency.
 8. The compressor of claim 1, wherein the stator includes a plurality of teeth, and the winding is wound on the teeth via insulating material.
 9. The compressor of claim 1, wherein the motor unit starts working as an induction motor, and when its rotation becomes near a synchronizing rotation, synchronous pull-in is carried out for synchronous operation. 